Exposure of mammalian muscle to the local anesthetic drug bupivacaine (Marcain) is followed by a rapid degeneration followed by regeneration. The greater part of this project concerns the development of this model for further investigation of the regeneration of mammalian muscle. Using this drug a technique has been devised for the production of high-yield cultures of rat skeletal muscle myoblasts and fibers. These cultures are to be employed in investigating the specificity of fusion between genetically labelled myoblasts of fast and slow muscles and the effects of substances of neural origin on the differentiation of cultured muscle fibers. An electron microscopic study of cell survival and multiplication during the initial degenerative stages in adult fibers is to be carried out. The mdoel will also be used to explore the effects of programmed chronic stimulation on the further differentiation of denervated regernerating skeletal muscle. An initial electrophysiological study is being carried out to establish basic data about membrane potentials, miniature end-plate potentials and acetylcholine sensitivity of both innervated and denervated regenerating fibers. The effect of bupivacaine on the survival of free autogenous muscle transplants has also been studied.